Dave probably knows more than everyone thinks. Usually if you've got a lot of ink, you know a lot about it. Even if you've just picked it up in the 4883277963+ hours they've spent in the shop. He may be the critique on looks or something though while the others focus on the technical aspects.
I haven't watched that how yet... wanted to but when I saw Dave was a judge i was like... why. i guess he's a wildcard judge. Those ones where they have no real experience and just go off of what they like.